1. Field of the Invention
The present invention relates to a method of manufacturing III-V nitride compound semiconductor by hydride vapor phase epitaxy (HVPE).
2. Background Art
III-V Group nitride compound semiconductors represented by the general formula InxGayAlzN (where 0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1) can be adjusted in direct band gap energy by varying the III Group element content. As this makes them adaptable to optical energies of wavelengths from ultraviolet to red, they are usable as high-efficiency light-emitting element materials over a range extending from ultraviolet to visible light. Moreover, since they have a larger band gap than Si, GaAs and other such semiconductors widely used up to now, they can maintain the characteristics of a semiconductor up to high temperatures at which conventional semiconductors cannot operate. This property is basically utilizable to fabricate electronic devices with excellent environmental resistance.
Owing to the very high vapor pressure of the III-V Group nitride compound semiconductors in the vicinity of the melting point, however, growth of a large crystal is extremely difficult and a crystal of a size practical for use as a substrate for fabricating semiconductor chips cannot be obtained. The general practice in fabricating compound semiconductors is therefore to use a substrate of Si, GaAs, SiC, sapphire, ZrB2 or other material that has a crystal structure similar to the compound semiconductor and enables large crystal fabrication and to epitaxially grow a desired single crystal thin-film layer on the substrate. Relatively good quality crystals of these compound semiconductors have now become obtainable by using this method. By using the metalorganic vapor phase epitaxial (MOVPE) method to conduct growth using a buffer layer, it is generally possible to achieve a half-value width for (0004) of around 200 seconds as measured from the x-ray rocking curve.
On the other hand, hydride vapor phase epitaxy (HVPE) compares favorably with other methods of growing compound semiconductor in the points of high growth rate and ability to achieve high-purity crystal growth by suppressing incorporation of impurities. However, HVPE lags behind MOVPE and other methods in the establishment of a heteroepitaxial method enabling two-stage growth using a buffer layer. In actual practice, a thin film of around 3 μm thickness grown by MOVPE or the like is used as a base layer and a thick layer of the compound semiconductor is homoepitaxially grown on the base layer by HVPE. As cracking occurs even when homoepitaxial growth is conducted by HVPE, however, it is difficult to obtain high-quality crystal over a wide area. Other drawbacks have also come to light, such as that crystallinity of the grown layer is inferior to that of the base layer, as evidenced by the fact that the half-value width of the x-ray rocking curve (XRC) of the grown layer is broader than that of the base layer.